**RADIAN AND STERADIAN:**

**Radian:** The radian is the measure of a plane angle. One radian is defined as a plane angle with its vertex at the centre of a circle of radius r which is subtended by an arc whose length is equal to r.

**Steradian**: It is the measure of a solid angle. It is defined as the solid angle with its vertex at the centre for a sphere of radius r which is subtended by a spherical surface area equal to the area of a square, whose side length is r.

**SOLID ANGLE: Continue reading “”**